The technology underlying the design of bicycle wheels has evolved in recent years. For many years, sturdiness and ease of manufacture were the primary driving forces underlying the design of a bicycle wheel. However, increasingly, bicycle wheels, and especially bicycle wheels designed for racing purposes, are being designed to be light-weight and aerodynamically efficient.
A variety of techniques have been used to achieve lighter weights, with most of the design efforts being centered in the choice of materials from which the bicycle wheel is made. Traditionally, bicycle wheels were made from a steel extrusion bent into a circular hoop. However, in order to make the wheels more light-weight, lighter weight metals, such as aluminum, and exotic metals such as titanium and other alloys have been substituted for steel. Additionally, significant weight savings can be achieved through the use of strong, light weight non-metallic materials, such as carbon fiber composite materials. Examples of such carbon fiber wheels are the wheels produced by Compositech, Inc. of Speedway, Ind. under its ZIPP® Speed Weaponry® brand.
Another technology improvement that has come to the fore in recent years is to shape the wheels in a manner that increases aerodynamic efficiency. To achieve this result, a wide variety of different wheel shapes have been produced. The object of most of these designs is to better control the flow of air over the wheel to reduce the aerodynamic drag of the wheel.
One example of such an aerodynamic wheel is the disc-type bicycle wheel. A disc wheel is unlike a traditional wheel in that it has no spokes. Rather, the disc wheel typically has a center hub for mounting the wheel to a bicycle frame, a radially outwardly facing tire engaging portion, and first and second opposed, radially extending, axially facing side surfaces. The side surfaces are disc-shaped, have no significant open spaces, and extend between the hub and the tire engaging surface. On a disc wheel, the side surfaces are generally continuous, to leave no voids between the hub and tire engaging surface. An example of such a disc wheel is the ZIPP® 900 Disc Wheel, manufactured by Compositech, Inc. Disc wheels have been found to be especially useful on bikes used on racing tracks and events where riders ride against the clock, as their light weight and aerodynamic efficiency, help to increase a riders' ability to achieve and maintain high speeds.
Another technique for increasing aerodynamic efficiency is to increase the radial extent of the side surfaces of a rim-and-spoke type wheel, to produce a “deep section” type wheel. As a point of comparison, a typical bicycle rim of a rim-and-spoke type wheel has a side surface with a radial extent of approximately one half inch or less. In most cases, the radial extent of the rim is only slightly larger than the radial extent of typical caliper of a bicycle brake pad. By contrast, a deep section type rim may have a radial extent well over one inch, and often two inches or more. Examples of such deep section rims are the ZIPP® 404 rim, which is also manufactured by Compositech, Inc., and the rims shown in Sargent, U.S. Pat. No. 5,975,645; and Hed et al., U.S. Pat. No. 5,061,013. The theory behind the use of such deep section rims is that the increased radial extent of the side surface of the rim creates an airfoil shape which reduces the aerodynamic drag of the wheel.
A further technique for reducing aerodynamic drag of a bicycle wheel involves reducing the number of spokes on the bicycle wheel and making the spokes more aerodynamically shaped. Typically, racing wheels have significantly fewer spokes than non-racing wheels. By reducing the number of spokes, it is believed that the turbulence created by the wheel is reduced, thereby reducing the aerodynamic drag of the wheel.
Although the above-mentioned techniques and wheels do provide a significant improvement in aerodynamic efficiency, when compared to standard wheels, room for further improvement still exists. In particular, room for improvement exists in increasing the aerodynamic efficiency even further.
One object of the present invention is to provide a wheel with a more aerodynamically efficient surface to help further reduce drag, when compared to wheels of similar shape and weight.